last time my cild used to wake up at 3am ...sometimes 4 am and cry for no reason n cannot be comforted... this goes on for months... then it just stop...
Im tinking maybe due to over excitment during the day.

This could be night terror. The pattern keeps repeating itself every night. My son used to wake up at 10pm every night crying hysterically and unconsolably. What you need to do is to wake your child up just before the episode happens again (ie before 3am) to break the pattern.

Judging from the scenario, it could be night terror. I got a similar situation too and I though my DD got possessed by dirty things, even gone to extent of placing a glass of water at the corner of the room to test (anxious parents); in the end turn out to be nothing.

Mine woke up, started crying non-stop at 2am every night. Realised she probably felt in-secure, everynight standby her side until 3am to ensure she does not cry... when she does, just whisper into her ears that mummy is here and pat her back to sleep, it took me a month to ensure the situation does not repeat again.